CDN Network - Interview Tips

Interview Approach

Initial Questions (5 min)

Content Types: Static, dynamic, video?
Geographic Coverage: Global or regional?
Scale: How many requests per second?
Latency: What's acceptable latency?
Security: DDoS protection needed?

Design Progression

Step 1: High-Level (5 min)

Users → GeoDNS → Edge Locations → Origin

Step 2: Edge Architecture (5 min)

Cache servers at edge
GeoDNS routing
Anycast for single IP
Multi-tier caching

Step 3: Caching Strategy (5 min)

Cache-Control headers
TTL-based expiration
Purge API
Cache warming

Step 4: Routing (5 min)

GeoDNS for geographic routing
Health-based routing
Performance-based routing
Failover logic

Step 5: Security (5 min)

DDoS protection at edge
WAF for application security
SSL/TLS termination
Rate limiting

Step 6: Scaling (5 min)

Add edge locations
Increase capacity per edge
Origin shield
Auto-scaling

Key Topics

Must Cover

✅ Edge locations and POPs
✅ GeoDNS routing
✅ Caching strategy
✅ Origin protection
✅ Failover

Should Cover

✅ DDoS protection
✅ SSL/TLS termination
✅ Cache invalidation
✅ Performance optimization

Talking Points

GeoDNS Routing

"We use GeoDNS to route users to the nearest edge location based on their IP address. This minimizes latency by serving content from geographically close servers."

Caching Strategy

"We cache static content with long TTLs (hours to days) and dynamic content with short TTLs (seconds to minutes). Cache-Control headers from origin determine caching behavior."

DDoS Protection

"We absorb DDoS attacks at the edge using our massive distributed capacity. Anycast routing distributes attack traffic across all edge locations, making it difficult to overwhelm any single location."

Origin Shield

"Origin shield is an additional caching layer between edge and origin. It collapses multiple edge requests into single origin requests, protecting origin from traffic spikes."

Time Management

0-5 min: Requirements
5-15 min: Architecture
15-25 min: Deep dive
25-35 min: Scaling/security
35-45 min: Follow-ups

This guide helps you approach CDN design interviews with confidence.